1. Field of the Invention
The present invention relates to a compensation method for detecting the seeking speed of an optical disk drive and more particularly to an average compensation method of tracking error (TE) signals while the pick-up head of an optical disk drive seeks the tracks of an optical disk.
2. Description of the Related Art
For an optical disk drive to operate, an electromechanical actuator drives a pick-up head so as to focus laser beams to the surface of an optical disk. Then, any binary data stored is read and judged by the magnitude of the light rays reflected to a photo-detector; meanwhile, the reflective rays are used as servo control signals for driving the pick-up head. In other words, the laser beams are accurately focused on a right track, using such an optical signal to drive the pick-up head.
During the process of track seeking and track locking performed on optical disks, there is a sine waveform or a triangular waveform with a phase difference of approximately 90° between a TE (Track Error) signal and an RF ripple (RFRP) signal. For a DVD optical disk, the triangular wave mostly functions as the track error signal. As shown in FIG. 1, a digitized TE zero cross (TEZC) signal can be determined if the slice level of the track error is treated as a threshold, and the digitized RF ripple zero cross (RFZC) signal can be determined by means of the slice level of the RFRP signal. An optical disk drive calculates the number of tracks to be sought by the pick-up head, using the TEZC signal or the RFZC signal. In general, a half-track count with regard to the TEZC signal is performed with a clock counter, and then the seeking speed is derived from the count. The detected value of the seeking speed assists the feedback control of the seeking speed of the pick-up head.
FIG. 2 is a waveform diagram of the distorted driving signals for an optical disk drive due to the shift in a slice level. In comparison with FIG. 1, FIG. 2 shows that, owing to the slice level shift, both the upper half cycles and the lower half cycles (relative to the slice level) of the TE signal and the RFRP signal are asymmetric, leading to the distortion of the TEZC signal and RFZC signal; as a result, alternate half-track speed fluctuates. If the servo control system executes speed feedback or speed-related control procedure by means of the aforesaid distorted half-track speed, the control exercised by the pick-up head and the accuracy thereof deteriorates inevitably.